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Emdrive Electromagnetic Drive For Chinese Space Ships?
Tired of those conventional space drives that require some sort of reaction mass? Chinese researchers claim to have confirmed the basic principles behind the Emdrive - an electromagnetic drive concept that converts electrical energy into thrust using microwaves.
The Chinese are currently building a demonstration model to see if it works.
('Emdrive' Electromagnetic Space Drive)
Take a look at the explanation offered on Roger Shawyer's Emdrive website:
The principle of operation is based on the well-known phenomenon of radiation pressure. This relies on Newton’s Second Law where force is defined as the rate of change of momentum. Thus an electromagnetic (EM) wave, travelling at the speed of light has a certain momentum which it will transfer to a reflector, resulting in a tiny force.If the same EM wave is travelling at a fraction of the speed of light, the rate of change of momentum, and hence force, is reduced by that fraction. The propagation velocity of an EM wave, and the resulting force it exerts, can be varied depending on the geometry of a waveguide within which it travels. This was demonstrated by work carried out in the 1950’s. (CULLEN, A.L. ‘Absolute Power Measurements at Microwave Frequencies’ IEE Proceedings Vol 99 Part 1V 1952 P.100)
Thus if the EM wave travelling in a tapered waveguide is bounced between two reflectors, with a large velocity difference at the reflector surfaces, the force difference will give a resultant thrust to the waveguide linking the two reflectors. If the reflectors are separated by a multiple of half the effective wavelength of the EM wave, this thrust will be multiplied by the Q of the resulting resonant cavity.
The inevitable objection raised, is that the apparently closed system produced by this arrangement cannot result in an output force, but will merely produce strain within the waveguide walls. However, this ignores Einstein’s Special Law of Relativity in which separate frames of reference have to be applied at velocities approaching the speed of light. Thus the system of EM wave and waveguide can be regarded as an open system, with the EM wave and the waveguide having separate frames of reference.
The beauty of engineering is that you can actually build something to test it; we'll find out soon enough if Emdrives will power space craft.
In the meantime, you might want to compare the Emdrive explanation with other famous pseudo-scientific science-fictional space drives. See the entries for the spindizzy from James Blish's Cities in Flight and of course the elegant infinite improbability drive from Douglas Adam's Hitchhiker's Guide to the Galaxy .
Via Wired; see also the Emdrive website.
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